A typical prior art head and disk system 10 is illustrated in block form in FIG. 1. In operation the magnetic transducer 20 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer 20, usually called a “head” or “slider,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) in the magnetic medium included in the thin films 21 and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. The magnetic transducer 20 is positioned over points at varying radial distances from the center of the disk 16 to read and write circular tracks (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded. The magnetic domains in the media on can be written longitudinally or perpendicularly. The read and write head portions of the slider are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive.
In a disk drive using perpendicular recording the recording head is designed to direct magnetic flux through the recording layer in a direction which is generally perpendicular to the plane of the disk. Typically the disk for perpendicular recording has a hard magnetic recording layer and a magnetically soft underlayer. During recording operations using a single-pole type head, magnetic flux is directed from the main pole of the recording head perpendicularly through the hard magnetic recording layer, then into the plane of the soft underlayer and back to the return pole in the recording head. The shape and size of the main pole and any shields are the primary factors in determining the track width.
Perpendicular magnetic recording is considered to be superior to longitudinal magnetic recording for ultra-high density magnetic recording. The increase demand for higher areal density has correspondingly led to increase demand to explore ways to reduce the width of the write pole piece, increase the write field strength, and improve the write field gradient. Experimental evidence and modeling have shown that a trailing shield single pole writer (SPT) design achieves a 4-5 dB media signal to noise advantage over writing with the trailing edge of an unshielded pole, increase in dHy/dx of the head field, reduce partial erasure, and improve saturation. These features improve transition sharpness (linear resolution) and permit higher coercive field media (improved stability).
Lead overlay designs for read sensors provide an advantage in improved stability and amplitude. The primary problem is the wide MRW. In this design, track width controlled by the separation of the electrically conductive leads on top of the sensor is smaller than the full width of the sensor. The lead overlay design moves the track edges away from the active sensor region. A prior art spin valve head 12A with overlaid leads is illustrated in FIG. 2 in a section view taken parallel to the air bearing surface (not shown). The leads 36a, 36b as shown in this particular embodiment include three sublayers: tantalum 37, chromium 38 and rhodium 39. The tantalum and chromium layers serve as seed layers for the rhodium. The leads are deposited in contact with the top surface of the spin valve sensor 35 and the hard bias structures 33a, 33b. The gap layer 31 underlies the two hard bias structures 33a, 33b and the sensor 35. The hard bias structures 33a, 33b are shown as a single element even though they include more than one layer, e.g., a chromium layer (not shown) followed by a CoPtCr layer (not shown). The spin valve 35 is also illustrated as a single entity for simplicity even though it includes several layers.
In published U.S. patent application 20040257713 by Pinarbasi, et al., Dec. 23, 2004, a lead overlay magnetoresistive sensor is described with leads having substantially vertical end walls to accentuate sense current near the ends of the leads. Insulating layers isolate the hard bias layers from the path of the sense current. After a first photoresist liftoff structure has been removed, a second layer of photoresist is formed and patterned. The second layer of photoresist does not have the usual undercut liftoff structure. Instead, the second layer of photoresist has substantially vertical walls. Lead material may be conveniently chosen from low resistance, substantially inert conductors such as rhodium, gold, ruthenium, and the like.
In published U.S. patent application 20030011943 by Webb, et al., Jan. 16, 2003, various embodiments of spin valve sensors with overlaid leads are described. A first embodiment for a bottom spin valve deposits a cap layer over the sensor then “notches” to expose the outer edges of the sensor. The overlaid leads are deposited in contact with the exposed side of the sensors. A second embodiment “notches” down through the free layer, as well as, the cap then refills with copper and NiFe before depositing the overlaid leads. A third embodiment “notches” down through the free layer and partially into the spacer and refills with NiFe before depositing the overlaid leads. A fourth embodiment “notches” down through the free layer and completely through the spacer and refills with NiFe before depositing the overlaid leads. A top spin valve embodiment notches through the cap, AFM layer and optionally into or through the pinned layer before forming the leads that contact the pinned layer.
In published U.S. patent application 20050007706 by Dovek, et al., Jan. 13, 2005 describes a design in which an additional antiferromagnetic layer is added under the overlaid leads in a bottom spin valve design. The extra antiferromagnetic layer extends over the hard-bias pads onto the top of the spin valve and is coterminous with the lead material. The longitudinal bias provided by the hard-bias pads extends, it is said, without attenuation right up to the edges of the leads, so that the physical and magnetic widths of the sensor are essentially identical.